StarDate

Like a housecat after a nap, the universe is stretching its legs. Thanks to the Big Bang in which it was born, the universe is expanding rapidly. Astronomers see that expansion when they look at distant galaxies. Light from these remote objects is stretched to longer wavelengths. How much the light has been stretched reveals a galaxy’s distance.

This effect is known as the cosmological redshift. It stretches lightwaves to longer, redder wavelengths. For the most-distant galaxies, the stretch is huge. Wavelengths that originally were in the ultraviolet — which are much shorter than visible light — have been stretched into the infrared — wavelengths that are longer than visible light.

So the best way to study the very early universe is with infrared telescopes — especially space telescopes, which are above Earth’s infrared-absorbing atmosphere.

The redshifted light of distant galaxies tells us how fast the universe is expanding. The farthest galaxies appear to be moving faster than light. That’s because space itself is expanding faster than light — something that’s allowed by Relativity.

Plotting galaxies at different distances reveals how the rate of expansion has changed. This technique has helped show that the universe is expanding faster today than in the distant past — the result of a mysterious “dark energy.” It may continue to expand faster and faster as it ages — an ever-wider “stretch” that will continue forever.

Script by Damond Benningfield

The Milky Way arches high overhead on December evenings. This hazy band of light outlines the disk of our home galaxy. As night falls, it passes from the Northern Cross, which is in the west, to W-shaped Cassiopeia high in the northeast, and down near the face of Taurus, the bull, in the east.

The Milky Way glows a little more softly at this time of year than it does in summer. We’re looking away from the galaxy’s crowded center and toward the thinly settled edge of its disk. And beyond that is the halo — an extended volume of space that contains some of the galaxy’s oldest stars.

Astronomers classify the stars in the halo as Population II, while most of those in the disk are Population I. The difference isn’t just where the stars reside — it’s what they’re made of.

All stars consist mainly of hydrogen and helium, the two lightest elements, which were created in the Big Bang. But they also have a smattering of heavier elements. Most of these elements were created in the hearts of other stars, then hurled into space as the stars died. Eventually, some of the elements were incorporated into new stars and planets.

Population II stars formed when there were almost no heavier elements around, so they have only tiny amounts of them. But Population I stars — stars like the Sun — are younger, so they have higher proportions of heavy elements. It’s still not much, but it’s enough to set these stars apart from their older kin.

Script by Damond Benningfield

A big dust storm blanketed the planet Mars for much of this year, hiding much of the surface from view. And it turns out that Mars isn’t the only world besides Earth that has dust storms — so does Titan, the largest moon of Saturn.

Titan is the only moon in the solar system with a dense atmosphere. Clouds waft through the sky and produce rains that fill rivers and lakes. Titan is so cold, though, that the liquid isn’t water. Instead, it’s ethane and methane.

Titan also has large dune fields along its equator. The dunes are made up of grains of frozen hydrocarbons.

In 2009, the Cassini spacecraft saw some bright spots above the equator that were hundreds of miles long. They lasted from about half a day to several weeks.

Scientists originally thought the spots were patches of clouds. But a deeper analysis found that the spots weren’t the right composition or at the right altitude to be clouds. Instead, they probably were dust storms.

The storms required especially strong wind gusts — up to about 20 miles per hour. And they might have blown some of the dust far away from the equator — creating a light dusting across this intriguing moon.

And Saturn is near our own moon tonight. They’re quite low in the southwest at sunset, so there’s not much time to look for them. Saturn looks like a bright star close to the upper left of the Moon. If you miss them tonight, try again tomorrow night, when Saturn will stand to the lower right of the Moon.

Script by Damond Benningfield

Saturn is disappearing from view. It’s quite low in the southwest as night begins to fall, so even though it’s pretty bright, you need a clear horizon to spot it.

But an object that’s named for Saturn is still in good view. The Saturn nebula stands about half way between Saturn and the brighter planet Mars, which is in the south. The nebula is above Capricornus, in a remote corner of Aquarius.

Through binoculars, the nebula looks like a fuzzy green star. A small telescope reveals an outline that resembles the planet Saturn — hence the nebula’s name.

The Saturn nebula is the final gasp of a star. As the star neared the end of its life, it puffed up to giant proportions. Changes in its core caused those layers of gas to puff out into space. Today, they continue to expand. They form a colorful and complicated bubble around the star’s core.

The bubble consists of a couple of shells of gas and dust. The inner shell is catching up to the outer one, creating shockwaves. Jets of gas shoot out from the poles of the star’s core. They punch through the bubbles, and form dense clumps as they ram into the material around the dying star.

Over tens of thousands of years, the bubble will grow thinner and thinner. And the star’s core, which produces the energy that causes the nebula to shine, will get cooler and fainter. So the Saturn Nebula will disappear, and only the dead core will remain — a tiny cosmic ember known as a white dwarf.

Script by Damond Benningfield

The big dog trots across the southern sky on these late-autumn nights — the constellation Canis Major. It’s conspicuous thanks to its leading light: Sirius, the Dog Star — the brightest star in the night sky. It climbs into view in the southeast by about 10 p.m. right now, but it’ll rise earlier as autumn gives way to winter.

Canis Major is escorted across the sky by the little dog, Canis Minor. It’s to the upper left of the big dog in late evening.

Under a fairly dark sky, it’s not hard to see Canis Major as a four-legged animal. But Canis Minor is another story. On most charts, it’s drawn as a single line connecting two stars.

One of those is quite easy to spot, though, because it’s also one of the brightest stars in the night sky: Procyon, a star whose name means “before the dog.” The name indicates that, from mid- to high-northern latitudes, which includes most of the United States, Procyon rises before Sirius.

Like Sirius, Procyon is a close neighbor — in this case, a bit more than 11 light-years away. The star itself is similar to Sirius, which means it’s bigger, hotter, and brighter than the Sun.

And also like Sirius, it has a “dead” companion — a white dwarf. The companion was born more massive than Procyon, so it burned out more quickly. The companion is too faint to see without a telescope. And even with a telescope, it’s so close to Procyon that it’s quite difficult to spot through the glare.

Script by Damond Benningfield

Neptune is a forgotten giant. It’s the fourth-largest planet in the solar system — almost four times the diameter of Earth. Yet it’s so far away that we need help to see it. Out of sight, out of mind.

For the next few nights, though, you can get a good idea of where Neptune is by following a bright point of light — the planet Mars. The Red Planet is well up in the south at nightfall, and looks like a bright orange star.

Tonight, Neptune is about a degree to the upper left of Mars — less than the width of a finger held at arm’s length. Mars will move much closer to Neptune tomorrow night, then slide just past it by Thursday night.

Under dark skies, Neptune is just visible through strong binoculars. But for the best view you need a telescope. The planet looks like a small, faint star, with a hint of blue.

Mars passes by Neptune every couple of years or so. It takes Mars that long to make a full loop against the background of stars.

Neptune doesn’t move nearly that quickly, though. That’s because its average distance from the Sun is about 2.8 billion miles — roughly 20 times farther than Mars is. At that range, it takes 165 years for Neptune to complete one turn through the sky.

Again, look for Mars in the south as the sky gets good and dark, and sliding down the southwestern sky later on. And if you have dark skies and some help, take a look for Neptune, too — a forgotten giant near the Red Planet.

Script by Damond Benningfield

It’s looking like a busy summer in Antarctica. NASA plans to launch several giant balloons from the continent to study the universe.

The launch window for these missions opens in early December, when the weather generally becomes calm and clear.

Air currents form a vortex around Antarctica. A balloon launched into that vortex circles the continent. When the mission is done, its payload parachutes onto the ice.

Mother Nature doesn’t always cooperate, though. Last year, the only planned mission had to be abandoned after 16 launch attempts were wiped out by bad weather. The payload was left in Antarctica for another go this year.

That payload is known as SuperTiger. Its mission is to catch and analyze the heaviest cosmic rays — the nuclei of heavy atoms blasted into space by supernovae. Studying these elements can help astronomers understand what happens inside the exploding stars.

A mission known as X-Calibur will look at the X-rays produced by black holes and neutron stars — the corpses of supernovae. The observations should reveal details about how black holes gobble up material from companion stars.

And a third mission, known as Barrel, will study space weather. In particular, it’ll look at how energetic particles spiral toward the surface from Earth’s radiation belts.

Script by Damond Benningfield

When Hubble Space Telescope was launched, it had a big problem: It couldn’t see very well. NASA had allowed it to fly with a flaw in its main mirror, which blurred its view of the cosmos. But 25 years ago this week, a crew of astronauts set out to fix the problem.

The crew of mission STS-61 grabbed Hubble from orbit and secured it in the shuttle’s cargo bay.

During five spacewalks, the astronauts installed a set of corrective lenses and a new camera to sharpen Hubble’s view. They also replaced Hubble’s solar panels. The old panels “flapped” as their temperature changed, creating a jiggle in the telescope. And they replaced or upgraded gyroscopes, computers, and other systems. They then released the telescope to continue its work.

The repairs were a big success. Hubble began snapping remarkably clear pictures of the universe.

Four more servicing missions followed over the next 15 years. Each one improved Hubble’s capabilities. And the telescope is still working — thanks in part to the past visits from astronauts.

Script by Damond Benningfield

A beautiful triangle will greet early risers tomorrow: the Moon, the planet Venus, and the star Spica. They’re in good view as the first blush of twilight paints the sky.

The Moon is a waning crescent right now. The “crescent” part is pretty obvious — sunlight illuminates only a sliver of the lunar hemisphere that faces our way.

It’s nighttime across the remainder of the lunar disk. It’s not an especially dark night, though, because the gibbous Earth hangs in the sky. Earth is bigger than the Moon is, and its surface reflects more sunlight. So a gibbous Earth provides many times more light than the full Moon offers here on Earth. And you can see the “earthshine” for yourself — it gives the dark portion of the lunar disk a ghostly appearance.

The Moon is “waning,” which means the bright crescent is getting smaller by the day. The Moon will disappear in the dawn twilight in a few days. And it’ll pass between Earth and Sun on Thursday night, when it’ll be “new.” It’ll then return to view a couple of nights later — this time in the evening sky, as a waxing crescent.

For now, look for the beautiful Moon before and during dawn. Venus, the brilliant “morning star,” will stand almost directly below the Moon tomorrow. And Spica, the leading light of the constellation Virgo, will stand a little farther to the lower right of the Moon. Venus and Spica will line up to the upper right of the Moon on Tuesday.

Script by Damond Benningfield

In the 1960s and ’70s, America and the Soviet Union sent dozens of missions to the Moon. Today, though, lunar exploration is a multi-national enterprise. In recent years, Europe, India, and Japan have all sent spacecraft to the Moon. And five years ago today, China entered the Moon business, too, with the launch of Chang’e 3, named for a Moon goddess. The craft landed on the Moon two weeks later, and deployed a small rover.

The next Chinese mission, Chang’e 4, is scheduled for launch this month. It was built as a backup for the earlier mission, but it’ll carry different instruments. And it has a different target as well — a place that no spacecraft has gone before: the Moon’s far side — the hemisphere that we never see from Earth.

If all goes well, the craft will land in South Pole-Aitken Basin. It’s about 1500 miles wide and eight miles deep. It was carved when a giant space rock hit the Moon billions of years ago.

Chang’e 4 will photograph the surroundings, listen for moonquakes, and analyze the lunar dust. And like its predecessor, it’ll deploy a rover to make additional observations.

To stay in touch with the mission, China launched a communications satellite earlier this year. It’s perched at a point in space where the gravity of Earth and Moon are balanced. That allows it to see Earth and the lunar farside at the same time. And next year, it’ll do some astronomy — monitoring radio waves from deep space.

Script by Damond Benningfield